But an idea of what their spaceships look like [at least the ones they attacked with] and what weapons they used probably would be known enough to say stuff like "Spaceships just imploded in the mere presence of their monolithic vessels", right? Even than with survivors you'd still have their accounts.

I mainly ask not because I wanna go on a interstellar adventure but because I imagine that if the tech gap is inferred to be small enough there'd be people who try bridging that gap pronto.